The invention relates to a dispersion-strengthened aluminium alloy exhibiting improved stability of strengthening at elevated temperature, and to a method of manufacture thereof.
Aluminium alloys are widely used as structural materials in weight critical applications, such as for aircraft construction. Strength is commonly achieved by alloying additions such as copper, magnesium, lithium or zinc to produce a dispersion of fine precipitates following suitable heat treatment. These conventional aluminium alloys have limited capability for use at elevated temperatures; or long term creep application they are generally not used at greater than 150xc2x0 C. for shorter term applications 200 to 300xc2x0 C. might be a more realistic limit to the working temperature range. The alloys arc limited in use by the limited strengthening exhibited at elevated temperature resulting from the tendency for precipitates to coarsen significantly as the temperature is raised. This reduces their effectiveness as strengthening phases at elevated temperature, and also their effectiveness as strengthening phases at room temperature after an elevated temperature treatment.
Significant developments have been made using rapid solidification techniques to introduce alloy elements that do not coarsen significantly at temperatures in excess of 200xc2x0 C. Examples of alloying elements most commonly used are Fe, V, Si . Ce etc. These approaches produce aluminium alloys with good strength at temperatures of up to 400xc2x0 C. However, they are difficult to fabricate because at temperatures exceeding 400xc2x0 C., the strengthening precipitates coarsen significantly and hence reduce their strengthening effectiveness. This means that the temperatures for forming components manufactured from such materials must be limited to less than 400xc2x0 C. Such constraints can impose significant limitations on the range of engineering components which can be effectively manufactured from these materials. Japanese patent publication number 082670075 and U.S. Pat. No. 5,632,827 both describe an aluminium material having ceramic dispersoids, which in both cases are formed by in situ development by precipitation during mechanical alloying and die formation respectively. EP 0751 228 relates to a titanium aluminium intermetallic having ceramic dispersoids also formed in situ. However, the size and dispersion of ceramic particles formed in this manner is difficult to control.